Storage devices such as magnetic disk devices (or hard disk drives (HDD)) are used in various apparatuses including portable electronic apparatuses such as desktop personal computers, notebook personal computers, servers, AV (audio and visual) equipments, and PDA (personal digital assistants), and electronic apparatuses for automobiles such as car navigation systems.
As the memory capacity of each HDD has increased, the recording density (the area density) of each magnetic disk is becoming higher, and the flying height of each head with respect to a magnetic disk is becoming very small. Also, the flying height of each head provided in each HDD with respect to a magnetic disk is controlled with negative pressure generated between the head and the magnetic disk. The value of the negative pressure is almost constant wherever the head is located, but slightly varies depending on the shape of the head floating face and the surface roughness of the magnetic disk. The variation of the head flying height caused by the variation of the negative pressure leads to a head crash due to head disk interference. Therefore, improvements have been made on the head floating face and the magnetic disk surface. The variation of the head flying height also affects read and write performances and head crashes, and its influence is becoming larger as the recording density is becoming higher.
On the other hand, in conventional cases, the floating characteristics of each head are designed so as to cancel variations caused by an air bearing slider (ABS) structure, rotational windage loss at radial positions on the magnetic disk, the value of the negative pressure, and the surface roughness of the magnetic disk.
Accordingly, when the flying height of the head becomes smaller, the HDI margin with respect to the magnetic space becomes narrower, and there is a possibility of a head crash. When the head collides with the surface of the magnetic disk, there is a possibility that a read error (thermal asperity) is caused by the heat generated by the collision. Furthermore, there is a possibility that some of the lubricant agent applied onto the surface of the magnetic disk moves on to the head due to contact between the head and the magnetic disk.
On the other hand, when the flying height of the head becomes larger, there are possibilities that the electromagnetic conversion characteristics efficiency becomes lower due to a magnetic space expansion, the reproduced output becomes lower, a read error is caused, and a seek error is caused by a servo signal read error.
To counter this problem, a technique has been recently suggested to control the flying height in the HDD. For example, Japanese Patent Application Publication No. 2005-71546 discloses a method for controlling a protrusion (a thermal protrusion) on the head floating face with respect to the magnetic disk. Also, Japanese Patent Application Publication Nos. 2003-168274, 2003-272335, 2006-4474, and 2006-18987 disclose methods for controlling the flying height of the head with respect to the magnetic disk by controlling heat generation of a heater. Japanese Patent Application Publication No. 10-241333 discloses a method for preventing thermal asperity by removing protrusions from the magnetic disk surface. Japanese Patent Application Publication No. 11-185210 discloses a method for detecting thermal asperity.
In recent years, the perpendicular magnetic recording method is used so as to maintain a stable recording state against a heat fluctuation phenomenon. By the perpendicular magnetic recording method, there is a stronger correlation between the write characteristics (the overwrite characteristics) and the read margin. Accordingly, the variation of the write characteristics caused by the variation of the flying height has greater influence on the read margin.
In conventional cases, however, the above described influence on the hard disk device is not taken into consideration when the head is controlled. As the recording density is becoming even higher in the future, there is fear that the influence on the data reading and writing performances and the likes in each hard disk device will become even greater.